Device for cooling of fluids and edible foams

ABSTRACT

The invention pertains to a device for the cooling of edible foams, where a cooling or freezing system for pre-freezing of the foam is directly outlet-connected to an aeration system, a motor driven extruder device designed as combined deep freezing and transport device is outlet-connected to the cooling and freezing system, in which the pre-frozen foam can be cooled down to storage temperature, and the aeration device, the cooling or freezing system and the extruder device are connected together by means of pipes. The device of the present invention is characterized in that the extruder device has at least one double screw system with two screws positioned parallel to each other with their rotational axes. The lands of the screws of the double screw system scrape against the inner cylinder mantle surface of the housing surrounding it. The threads of the second screw are centered between the threads of the first screw and an increased spacing of the rotational axes of the screws is created, so that the front side of the screw thread of the other screw facing the surface of the cylinder mantle of each screw, has a radial distance from it. The lands of the screws with the surface of the cylinder mantle of the screws and of the inner surface of the cylinder mantle of the housing .[.bounds.]. .Iadd.bound .Iaddend.an extremely flat screw channel.

BACKGROUND OF THE PRESENT INVENTION

In wide areas of the foods industry, foams are used for the productionof foods and/or luxury foods. These foams have in the first place, theadvantage that they increase the enjoyment value of the particularproduct, and secondly, the volume will be increased by beating in someair.

Two classical examples of these food foams are whipped cream and icecream. The volume of both products is increased to about double by theincorporation of air. The fine distribution of the air bubbles is anessential quality criterion both for ice cream as well as for whippedcream. In both the aforementioned products, it is only thisincorporation of air which makes the product suitable for consumption:

In whipped cream, the high fat content would essentially prohibit theproduct's consumption in its original liquid form.

In ice cream, the incorporation of air results in the ice creamattaining a creamy consistency; without the incorporation of air, it ismerely a solid-frozen block.

The technologies for continuous aeration (incorporation of air) inwhipped cream and ice cream manufacturing are known around the world.The technologies for whipped cream and ice cream do, indeed, differ fromone another significantly, but their basic principle is nonetheless thesame.

The distribution of deep-frozen products, and thus the sales of such,have more than doubled in recent .[.year.]. .Iadd.years.Iaddend..Although deep-freezing was used initially only to keep vegetables fresh,the entire range of foodstuffs is presently available in the form ofdeep-frozen versions of all goods also available in fresh form. Havingstarted with the deep-freezing of vegetables, the dissemination ofdeep-frozen food now ranges from ready-cooked meals to all types ofbakery goods. Within this range of deep-frozen goods, ice cream occupiesa special and significant rank. In fact, for ice cream this is the onlypossible marketing route, via a complete and uninterrupted deep-frozenchain. The industry has been making efforts to market cakes and gateauxon a whipped-cream basis in the form of deep-frozen products for somefifteen years. Continuously rising sales in this sector illustrate thegreat market potentials for this segment. The technology for manufactureof such deep-frozen cakes and gateaux is, however, largelyunderdeveloped, if one disregards the use of continuously operatingautomatic aerators.

Ice cream manufacturing technology has not undergone any furthersignificant technical changes since the introduction of continuouscooling and freezing systems (freezers). Here, work is still conductedon the same principles as were used thirty years ago, if one disregardstechnical modifications concerned solely with control of the ice creamcooling and freezing system.

The Current Procedure for Making Gateaux

In the procedure currently used in the manufacture of deep-frozengateaux, a suitable jelling agent is added to the mixture of whippedcream and sugar. This whipped cream is then pasteurized and matured inmaturation tanks for approximately 24 hours at +5° C. The cream is thenfed by means of a conveying pump to the continuously operating aerator.This aerator is simultaneously supplied with compressed air. Both fluidsare mixed with one another on a rotor-stator principle, resulting in thewhipped cream absorbing air.

The whipping of cream results in a three-phase system, comprising theair, fat and serum phases. Air bubbles are beaten into this emulsion(aeration). A portion of the fat particles .[.are.]. .Iadd.is.Iaddend.destroyed in the process. The fat is present at lowtemperatures partially in solid crystallized form, a small portion ofthe fat, however, still being trapped in liquid form in fat particles.The mechanical effects of the rotor-stator system result in thedisintegration of these fat particles. A portion of the free fatescapes. The beaten and the intact fat particles then accumulate on theair/serum boundary.

Due to their hydrophobic properties, parts of fat particles project outof the monomolecular layers of crystalline fat into the interior of theair bubbles. Free liquid fat serves to bind the solidified fat with it.In the serum phase, the number of intact fat particles decreases duringwhipping (aeration). The proteins remain in the serum phase. This cycleproduces a stable foam (whipped cream). This foam is then transferredlayer-by-layer into gateaux molds using a filling system. The foam has aconsistency which just permits transfer by means of volumetric feeders.The jelling agents present in the cream set only after several minutes,i.e., they form a structure within the structure of the foam, the fatparticles and the air bubbles being fixed in position by thesestructure-forming jelling agents. The water is also bound simultaneouslyto these jelling agents.

Following aeration and metered feeding of the cream into appropriatecake molds, these gateaux are transferred to a solidifying tunnel fordeep-freezing. During deep-freezing, the gateaux pass through an aircurrent at approx. -45° C., and yield their heat to this current of air,resulting in them having a center temperature of -18° C. after a coolingperiod of some two to three hours. In this relatively slow freezingcycle, the water present in the product freezes out in the form ofrelatively large crystals of ice. The formation of these ice crystalscauses the partial destruction of the structure previously formed by thejelling agent. It is also possible for crystals of ice growing duringthe freezing process to puncture the tiny air bubbles, thus destroyingthe membrane of these air bubbles. This is not a significantdisadvantage, provided the product remains frozen, i.e., the water ispresent in the product in solid form.

During thawing of the product, the solid water in the ice crystalstransforms into a liquid water phase. Concentration of the droplets ofwater occurs. The structure formed by the jelling agent and the emulsionconsisting of air, fat and serum can then no longer fully contain theseaccumulations of water, which are greater than those present in theinitial product, and the product becomes wet during thawing.

The relatively slow freezing process also results in the destruction ofa portion of the air bubbles. This damage in the product is irreparableand results in a reduction of product volume during thawing.

This problem can, indeed, be countered by means of increased addition ofjelling agents, a partial solution which, however, involves thedisadvantage of affecting the flavor of the product. Deep-frozen whippedcream treated in this way no longer retains its fullness of flavor afterthawing. Contrary to the situation with other foodstuffs, thedeep-freezing of whipped cream using the technology currently availabledoes not constitute a method of preserving its quality. On the contrary,deep-freezing impairs this product's quality.

The Present Manufacture of Ice Cream

Ice cream recipes normally consist of milk, skimmed milk, cream, milkconcentrate, milk powder or butter, and sucrose, glucose or dextrosefrom fruit products, which can be added, and of hydrocolloids which actas stabilizers (vegetable binding agents, alginates, carrageenates,carob bean flour, etc.).

For the manufacture of ice cream, the individual components are weighedto accord with a specific recipe and adjusted to a defined ratio. Theseindividual components are then mixed with one another in a mixingvessel. Mixing is completed after a fifteen minute period of mixing at63° C. Mixing is followed by pasteurization at 80° to 85° C. for aperiod of 20 to 40 sec. After this heat treatment, the mixture is cooledto approximately 70° C. and then homogenized in a two-stage homogenizer,at 150 bar in the first stage, and 40 to 50 bar in the second stage. Thefat particles are reduced in this process to below 2 μm.

This homogenization cycle is followed by cooling of the mixture down to2° to 4° C. The mixture is then transferred to tanks, where it isavailable for further processing following a maturation period of 2 to24 hours. This maturation period results in swelling of thehydrocolloids, hydration of the casein and an increase in viscosity, thestructure of the ice cream becoming finer. Resistance to melting andaeration are improved simultaneously, the fat crystallizes out and abalanced aroma is formed. After completion of the maturation cycle, thismixture is transferred to the cooling or freezing system for freezingand for simultaneous incorporation of air (aeration).

In present-day industrial practice, the mixtures for ice cream arepartially frozen in continuously operating cooling or freezing systems(freezers). A cutter shaft consisting of chromium-nickel steel rotateswithin a chromium-plated tube at a speed of approximately 200 rpm. Thecutters continuously scrape off a thin film of ice forming on therefrigerated internal wall of the tube and also ensure intimate mixingof the air fed in this cylinder.

FRIGEN (TM) or ammonia is generally used within a -25° to -30° C.temperature range for refrigeration of the cylinder from outside. Thesmall ice crystals desired necessitate high-speed freezing, which ismade possible by the highly cooled internal walls of the cylinder.

The mixture enters the freezing cylinder at a temperature ofapproximately 4° C. once the quantity of air necessary for aeration hasbeen metered into it. The air is beaten into the mixture at the pressureof approximately 3 to 5 bar normally present in the interior of thecylinder. The freezing process occurs simultaneously, and the ice creamleaves the cooling or freezing system in paste form. The maximumtemperature achievable using this process is -8° C.

The ice .Iadd.cream .Iaddend.produced in this way is packed into tubs orcornets. These products must then be subjected to an after-freezingprocess, in order to achieve their storage temperature of -20° C. Ifthis process is not applied, the water-ice crystals present in the icecream become larger, resulting in the ice cream having a rough andgritty flavor. The ice cream cooling and freezing systems currentlyavailable on the market do not permit temperatures lower than -8° C.

In the present state of the art, ice cream foams can be produced andfrozen down to approximately -7° C. But this temperature is not yet thestorage temperature. Rather, the storage temperature of -20° C. will notbe reached until after post-hardening in the deep-freezing tunnels. Tocarry out this method, large investment costs are necessary, inparticular for the deep-freezing tunnel. Moreover, the continuing energycosts are considerable. In the area of the manufacture of whipped cream,aeration methods are already known that operate exclusively in theabove-freezing temperature range. But the freezing of whipped creamfoams is entirely unknown in this case.

A New Method and Device for Cooling Edible Foams

In order to remedy the deficiencies described above, the method anddevice disclosed in German Patent No. 3,918,268 may be used. (ApplicantsHoffman and Windhab are co-inventors, along with two others, of thismethod and device, which are also the subject of co-pending U.S. patentapplication Ser. No. 07/777,375.) This method and device make itpossible for edible foams (e.g., ice cream and whipped cream) to becooled to storage temperature, e.g. to -20° C. in the same step, duringand/or in direct conjunction with the aeration. Thus for example, thewater present in whipped cream or similar items, will be frozen into icecrystals with a size less than 20 to 30 μm by extremely fast coolingwith simultaneous, dynamic stress. At a size of the ice crystals of 20to 30 μm, the danger that the product will exude moisture after thawing,is considerably less. Likewise, the air distribution in the product ismore stable, since an "injury" of the air bubbles is unlikely given thissize of ice crystal.

When using a high-speed freezing process of this type, the full flavorof the whipped cream can be retained, the fraction of jelling agent canbe reduced, and the approximation of a freshly produced product is muchgreater. Finally, due to the absence of a volume reduction, aform-stable product will be obtained which is of great advantage for theproduction of gateaux, for example.

Due to the combination of the aeration and freezing process, it is thusnow possible to simultaneously aerate and deep-freeze whipped cream on acontinuous basis. After-freezing of whipped cream products in ahardening tunnel by using cold air at about -45° C. is thus no longernecessary. Since the minimum temperature of -18° C. or less necessaryfor the deep-frozen products is attained in the production process, asubsequent freezing process has now become dispensable in any case.

In addition, when using this method, a fine distribution of watercrystals can be attained. When using this method, edible foams can thusbe produced on a basis other than on whipped cream, and due to thefreezing process they can be brought into a storable form. For example,this method may be used with fruit foams, e.g. foamed banana puree, andother milk products, such as, fruit yogurts or similar items.

Due to the use of this method, completely new foods can be produced in asimple manner with low consumption of energy or fuel, and these foodsare adapted to modern nutritional physiology. Such systems and processesare not known anywhere in the world. In this case, completely new foodmarkets will open up.

In addition, in the production of .Iadd.an .Iaddend.ice cream substance,in an application of this method, it can be whipped up and frozen at thesame time or immediately thereafter, so that it will no longer requireany post-hardening by means of cold air at -45° C., in order to achievethe final storage temperature of e.g. -18° C. or -20° C. Due to thismethod, the process of post-hardening of ice cream is eliminatedentirely, so that a continuous process run of freezing and filling ispossible, so that the products produced in this manner are ready to shipdirectly after product filling.

The cooling process (post-hardening) to -20° C. by means of cold air isin itself very investment-intensive from the system point of view-asdiscussed above--and very long cooling times are needed, since theaverage freezing of an ice cream product from 5° C. to -20° C.progresses at a rate of only 1 cm/h, so that for example, a 6 cm sizecube of ice cream will need a minimum treatment time with cold air ofthree hours to reach a core temperature of -20° C. In addition to thistime-intensive and system-intensive, previously known method, damage tothe product will also occur. At a temperature of -5° to -7° C., only 45to 63% of the existing water will freeze out. The remaining 40%, minusabout 5% water, remains as so-called "free water" in the product. This35% will not freeze until the post-hardening process. Now this waterwill shift toward the already existing water crystals and cause thesecrystals to increase in size. The larger the water crystals, the lesscreamy the taste of the ice cream. Due to post-hardening and theresultant growth in size of the ice crystals, a deterioration of thestructure of the ice cream will also occur. The structure changes fromcreamy soft, to hard, icy and brittle .Iadd.in .Iaddend.the extremecase. All these disadvantages will be avoided by application of thismethod.

Even though the starting materials of whipped cream and ice cream aretwo independent foods, the fundamental problem--namely the production offoams by aeration and freezing down to a temperature range where theyare storable, can be readily solved by the method according to theinvention.

Thus in the application of the method described above, it is nowpossible to produce frozen foams down to -18° to -20° C. in one workstep by beating (aeration) and then drawing it off continually in aready-to-ship form.

One particular advantage consists in the fact that the energy costs ofthe method by comparison to systems operating with post-hardeningtunnels in the production of ice cream, lie about 30% or more lower, sothat the method will operate particularly economically.

The aerated and frozen foam leaves the system on a continuous basis. Allparameters of manufacture of this foam are controllable, such as theoutlet temperature, quantity of input (beaten in) air, freezing speed.[.and.]..Iadd., .Iaddend.etc. Due to the control system, the device tocarry out the method itself remains in a process-stable state.

In the device described above, the product to be foamed up with air canbe aerated by air at 12° C. for example. The aerated product will thenbe cooled down in a refrigeration or freezer unit, to -5° C. forexample, and this will freeze the foam. The foam frozen in this manner,will then be further cooled down to -20° C. for example, in a suitableconveyor unit. The device components can be combined in a singleelement. The deep freezing tunnel is eliminated entirely by this device.

In particular, in the device disclosed in German Patent No. 3,918,268,the product to be foamed up is beaten in a device in which the foamedproduct is cooled down either simultaneously, or directly after leavingthe foam production unit, in at least one adjoining deep refrigerationdevice, and exits through an extruder screw and is immediatelyprocessed. The foam exiting from the extruder is ready to ship and doesnot need to be "post-hardened." In addition, several extruder devicesaccording to this state of the art, are run in parallel and/or insequence. For example, it is possible to let several extruders operatein the coextrusion process. The product fed to the aeration device canbe precooled. It is also possible to feed precooled foam to the deviceand then to cool down this foam to a storage temperature in the extruderdevice or in one or more apparatus components linked with the extruderdevice.

SUMMARY OF THE PRESENT INVENTION

The present invention addresses the problem of designing a device of thekind described above in such a manner that the product will be cooleddown to storage temperature on a continuous basis by a sensiblydesigned, relatively simple configuration, and can be homogeneouslystressed and well-mixed in the process, with a uniform and homogeneousremoval of heat.

These objectives are achieved by the present invention. In particular, adevice for the cooling of edible foams is provided, where a cooling orfreezing system for pre-freezing of the foam is directlyoutlet-connected to an aeration system, a motor driven extruder devicedesigned as combined deep freezing and transport device isoutlet-connected to the cooling and freezing system, in which thepre-frozen foam can be cooled down to storage temperature, and theaeration device, the cooling or freezing system and the extruder deviceare connected together by means of pipes. The device of the presentinvention is characterized in that the extruder device has at least onedouble screw system with two screws positioned parallel to each otherwith their rotational axes. The lands of the screws of the double screwsystem scrape against the inner cylinder mantle surface of the housingsurrounding it. The threads of the second screw are centered between thethreads of the first screw and an increased spacing of the rotationalaxes of the screws is created, so that the front side of the screwthread of the other screw facing the surface of the cylinder mantle ofeach screw, has a radial distance from it. The lands of the screws withthe surface of the cylinder mantle of the screws and of the innersurface of the cylinder mantle of the housing .[.bounds.]. .Iadd.bound.Iaddend.an extremely flat screw channel.

The device according to the invention for deep freezing--preferably tostorage temperature--of ice cream or other fluids down to temperaturesof less than -10° C. with simultaneous production of a creamy condition,implements an essentially homogeneous, mechanical energy input, based onthe use of a special double screw system.

The device of the present invention has the following significantfeatures:

a) The screws carry out a slightly opposing meshing motion;

b) The screw channel is designed so that, depending on the flow behaviorof the substance being treated, nearly no "flow dead zones" are created,and thus a homogeneous, mechanical energy input will be assured. Thelocal, mechanical energy input specifics the size of the producedstructural units--for example, ice crystals--and thus the quality of theproduct--for example, the creaminess; .Iadd.and .Iaddend.

c) The removal of heat from the material takes place preferably in ahomogeneous manner (inner and outer cooling).

In order to ensure properties a) to c) presented above, the device hasthe following preferred properties:

1. The screw channels of the double-screw system are of an extremelyflat design, with the ratio of the channel height (H) to the channelwidth (W) for each screw (H/W) is in the range 0.1-0.2, for example. Thescrew pitch is likewise small. The screw pitch angle ⊖ is 20° to 30°.

The precise selection of H/W and ⊖ is established under consideration ofthe flow function τ (γ) for the product at the correspondingtemperature. In this case it is important that the effective, minimumshear stress on the screw shaft and on the outer cylinder wall, exceedsthe yielding point τ_(o) of the material.

In this case it must be taken into account that a temperature gradientexists across the height of the screw channel, that is, the materialyielding point is a function of the channel radius.

Yield function τ (γ, υ) or yielding point τ_(o) (υ) are to be determinedin rheological measurements (υ=temperature; γ=shear rate).

2. The double screw system is preferably cooled directly via a fluidevaporating at the surface of the outer mantle, as well as possibly byan interior cooling of the screw. On the outer mantle of the screwchannel, a direct "flooding system" or a "flow-through principle," isimplemented, for example, by means of holes drilled in the outercylinder for refrigerant.

3. For an optimum generation of a creamy material system, for example,ice cream that contains a large fraction of dispersed air, it isnecessary to ensure the presence of gas during the mechanicaldeep-freezing treatment process in the double screw system. In thiscase-as will be discussed in further detail below-the double screw shaftcan be sealed by a gas-tight rotating mechanical seal.

In addition to the aforementioned design features, to produce thedesired, creamy structure of the deep-frozen material system, it is alsonecessary to take into account certain "operating criteria."

This includes in particular, the proper dimensioning of the mechanicalenergy input by selection of an appropriate RPM (depending on the screwgeometry). The mechanical energy dissipated in the material system--thatis, converted into heat energy--must not exceed a critical value that isspecified by the maximum possible heat dissipation established by thecooling system.

In order to ensure this, in a preferred device according to the presentinvention, to achieve a consistent end product, the speed of the doubleshaft system will be controlled as a function of the consistency (of theend product). The control and regulation unit disclosed in German PatentNo. 3,918,268 may be used in this regard.

Measurement of the consistency can take place here either via a directmeasurement in the end product (in-line viscosity measuring cell) orindirectly via the torque on a screw shaft, or by the power consumptionof the drive motor.

In summary, the deep-freezing stage in the device of the presentinvention consists of a double screw system turning in phase or incounter-phase, which will ensure a homogeneous mixing and mechanicalstress on the product to be processed, for example, ice cream. This isof decisive importance for the production of a very fine structure withsmall ice crystals and thus the desired creaminess, while at the sametime ensuring a large proportion of frozen-out H₂ O. At the same time, ahomogeneous stressing will be ensured by the selection of the screwchannel geometry and by the speed of the turning screw, in such a mannerthat a super-critical load on the "foam structure" of the aerated icecream of similar item is prevented, as also is the resultant structuraldisintegration (in particular: whipping loss).

Under consideration of the structure-related mechanical stress limits ofice cream or similar items, the geometry of the screw channel (and alsothe screw meshing) and the speed of the screw will also have to bedesigned with regard to an optimum heat transfer to the coolant underconsideration of the energy dissipation due to shearing of the ice creamor similar item.

According to the present invention, the input of mechanical energy intoan extremely flat screw channel under gentle screw meshing is performedessentially homogeneously (no local power peaks). In this case, H/W canbe≈0.1, where H=channel height and W=width of channel. As a rule, ascrew pitch angle e will be preferably chosen as 20° to 30°. Selectionof the screw speed takes place according to the formula, and per thisinvention, under consideration of the temperature-dependent yieldingpoint τ_(o) and also the critical shear stresses for structural change(aeration, loss of creaminess).

In referring to a "double screw system" or "double extruder" or "doublescrew" this does not preclude that "systems" of this type may be presentmore than twice, for example, four, six, eight or more times. "Doublescrew systems" of this or a similar type, can be positioned in paralleland/or in series in one or more housings.

In a preferred embodiment, the housing is a single piece and, in theregion of the inner surface of the cylinder mantle for the screws, hasseveral refrigerant channels positioned parallel to the axis andpositioned at a distance to each other. This allows refrigerant fluid toflow through these channels in a "flow-through principle."

In an alternative preferred embodiment, the housing of the two screws islocated in a container that can be filled with refrigerant in such amanner that the housing is externally "flushed." The refrigerant orevaporative fluid thus flows around housing walls of the double screwsystem as a direct "flooding system."

To provide for additional, inner cooling of the screw that can be usedtogether with a heating medium for thawing (end of test), screw shaftsof hollow design may be used.

In another preferred embodiment, each shaft end is sealed to the outsidefor the screws by a gas-tight seal designed in particular as a rotatingmechanical seal. This design allows for the optimized tailoring of

.Iadd.--.Iaddend.mechanical energy input.Iadd.;

--.Iaddend.homogeneous structural stress.Iadd.;

--.Iaddend.subcritical shear (minimizing of structuraldestruction).Iadd.; and

--.Iaddend..[.Cooling.]. .Iadd.cooling .Iaddend.gradient (takes accountof dissipated energy).Iadd...Iaddend.

The freezing process takes place by means of a scattering of mechanicaland thermal energy balance on the basis of the acquisition of atemperature profile of the material in the extruder and also the productconsistency as target parameter. The product consistency will bedetermined on the basis of on-line or in-line viscosity measurement.

The device of the present invention may also be provided with a controlunit which controls the speed of the screws specifically according tothe formula, under consideration of the temperature-related, criticalshear stresses for the structural changes for optimum tailoring ofmechanical energy input, homogeneous structural stress on the particularproduct, supercritical shear, cooling gradient and freezing process, bymeans of acquisition of the product consistency as target parameter. Theproduct consistency is determined by means of an on-line viscositymeasurement in such a manner that mechanical energy dissipated in thematerial system--that is, mechanical energy converted into heatenergy--does not exceed a critical amount.

According to this design, the selection of the screw speed takes placeaccording to a specific formula, with consideration of thetemperature-related, critical shear stress for the structural change perthis invention (loss of aeration, loss of creaminess). For example, atice cream outlet temperatures of about -15° C., according to thisinvention, for normal ice cream (about 10% fat percentage) a maximumshear gradient of 30 to 50 s⁻¹ will be created. In addition to theavoidance of supercritical stress, the energy input (dissipated) by theshear via the wall cooling per the invention, will be applied bydirectly evaporating refrigerant in addition to the melt enthalpy of thefreezing aqueous phase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Schematic illustration of a process flow as disclosed in GermanPatent No. 3,918,268;

FIG. 2: A section from FIG. 1, enlarged scale, partial cross section;

FIG. 3: Sectional views of the device disclosed in German Patent No.3,918,268;

FIG. 4: The double screw system of the present invention in partial,front view;

FIG. 5: A partial, longitudinal cross section of FIG. 4;

FIG. 6: The double screw system of the present invention includingrefrigerant channels in the outer cylinder of the screws for the flow ofa coolant fluid and also a screw inner cooling (partial cross section);

FIG. 7: Another embodiment of the present invention, wherein the doublescrew system is cooled via a fluid in a "flooding system" evaporating atthe outer mantle surface of the housing;

FIG. 8: A sectional representation of a screw according to the presentinvention with various geometric (design) relations; and

FIG. 9: A longitudinal cross section through a double screw system ofthe present invention (only one screw visible) with gas seal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It will be understood that the present invention can be implemented in anumber of different ways within the scope of the claimed inventionhereto. The presently preferred embodiment of the invention will now bedescribed.

Referring to FIG. 1, reference number 1 is an aeration device in whichthe product to be foamed is foamed through the admixture of (forexample) air. In the aeration device 1, the foam can have a temperaturee.g. of 12° C.

The foam produced in this manner leaves the aeration device 1 in thedirection of the arrow, and is fed to a refrigerator or freezer, inwhich the foam is cooled down to e.g. -5.5° C. The prefrozen foam 10 nowleaves the refrigerator or freezer 2 in the direction of the arrow andwill be fed to a combined extruder device 3. In the extruder device 3,the prefrozen, edible foam will be subcooled down to e.g. -20° C. forstorage, and leaves the combined extruder device 3 on a continuous basisas a finished, storable product 4 (foam), e.g. ice cream, whipped cream.

In FIG. 2, the combined extruder device 3 is shown schematically incross section. Reference number 5 denotes a shaft driven by a motor (notillustrated) that is connected to a rotor 6. The rotor 6 has severalvanes 7 that mesh at a distance with vanes 9 located on a stator 8. Theprefrozen foam 10 will be fed to a chamber 11 and thus to the vanes 7and 9. In this area, suitable cooling devices can be provided thatfurther subcool the prefrozen foam 10. The still thoroughly mixed foam10 will then be cooled .[.down.]. in an adjoining cooling device 12 downto storage temperature of e.g. -20° C. on a continuous basis in aone-pass method. Cooling coils 13 are indicated schematically in FIG. 2.The storable, cooled foam 4 will be transported away from the device 3continuously by one or more extruder screws 14. The extruder screw 14 isseated at its end section opposite the shaft 5, in a tubular housing 15merely indicated schematically, and can be driven by the same motor asthe shaft 5.

FIG. 3 shows detailed sectional views of the device disclosed in GermanPatent No. 3,918,268, for use in connection with the schematic flowpresented in FIG. 1. Reference number 1 denotes the aeration stage oraeration device; reference number 2 is the prefreezing stage or thecooling or freeing device, and reference number 3 is the deep freezingstage or the combined extruder device. The aeration device .[.2.]..Iadd.1 .Iaddend.consists essentially of a tubular housing 16 that hasan additional tubular housing 17 in the interior; it is positionedcoaxial to the outer housing 16, so that between outer and inner housing16 and 17, an annular space 18 remains; at the one end a coolant inletline 19 is connected, and to the other end, a coolant outlet pipe 20 isprovided. The coolant outlet pipe 20 is connected to a suitable line(not illustrated). The annular space 18 will thus have refrigerantflowing through. As refrigerant, a suitable brine, FRIGEN (TM) or thelike, may come into consideration.

In the inner, tubular housing, a rotor 21 is provided with numerousvanes 22 distributed across its perimeter and its length; these vanesare driven by a shaft 23 via a motor (not illustrated).

At the inner wall 24 of the inner housing 17, numerous vanes 25 are alsodistributed around the perimeter and along its length; these vanes meshwith the vanes 22 with a gap spacing.

On the one front side of housing 16 facing the shaft 23, a feed line 26is connected. On the one end 27 of this L-piece of the infeed line 26,the particular fluid, that is, the output component of the medium to befoamed, will be fed in, while a suitable foaming gas, air, as a rule, isfed into the feed line 26 through the pipe piece 28. Fluid and carriergas or air thus enter into the inner chamber 29 and are intensely foamedtogether by the vanes 22 and 25. The substances prefoamed in thisaeration device 1 leave the aeration device 1 via the pipe 30 in thedirection of arrow 31 and will be brought into the pipe 32 that isconnected to a housing 33 of the refrigerator or freezing device 2.

When flowing through the aeration device 1, fluid and carrier gas willbe precooled, and--as in all other stages, that is, aeration device 1,refrigerator or freezer 2 and deep freeze stage 3--coolant and fluid aremoving in counterflow to each other. In the refrigerator and freezerunit 2, the foam flows through an annular chamber 34 that is flushed onthe outside by coolant that is fed into an annular chamber 36 via aninfeed line 35, and then leaves this annular chamber 36 via a run-offline 37.

A rotor 38 is located coaxial to the annular chamber 34, 36; this rotoris driven via a shaft 39 by a motor. The prefrozen foam will bewithdrawn via a pipe 40 and sent to a housing 42 of the deep freezer viaa connection pipe 41. The housing 42 of the deep freezer stage 3 inturn, has an annular space 43 to which a line 44 is connected for theinfeed of coolant. The coolant leaves the annular space 43 via a line45.

Coaxial to the annular chamber 43 there is a motor-driven conveyor screw47 for example, that removes the deep frozen foam through a pipe 48. Thedeep frozen foam will then be processed, packed and transported off in asuitable manner.

Reference numbers 49, 50 and 51 denote thermocouples that can be used tomeasure the temperature of the deep frozen foam at various places in thedeep freezer stage.

In FIG. 3, V_(L) denotes the volumetric flow of the inlet fluid, V_(g)denotes the volumetric flow of the inlet carrier gas, and P_(g) denotesthe pressure of the inlet carrier gas at the pipe piece 28, Tm₁ denotesthe temperature in the inlet line 26, Md₁ the torque on the shaft 23, n₁denotes the speed of the shaft 23, TK₁ denotes the temperature in therefrigerant runoff pipe 20, Pm₁ denotes the pressure in the pipe section30, Tm₂ denotes the temperature in the pipe section 30, TK₂ denotes thetemperature in the coolant infeed line 19, TK₃ denotes the temperaturein the runoff line 37, Md₂ denotes the torque on the shaft 39, n₂denotes the speed of the shaft 39, TK₄ denotes the temperature in theinfeed line 35, Pm₂ denotes the pressure in pipe 40, Tm₃ denotes thetemperature in the pipe 40, Md₃ denotes the torque on the shaft 46, n₃denotes the speed of the shaft 46, Tm₅, Tm₆ and Tm₇ denote thetemperatures of the deep frozen foams measured by thermocouples 49, 50and 51 in the deep freezer stage, TK₆ denotes the temperature in theline 44, Pm₃ denotes the pressure in the pipe 48 and Tm₄ denotes thetemperature in the pipe 48.

Reference numbers 19, 20, 35, 37, 44 and 45 are for the single processstages that denote the particular refrigerant inlets and outlets. Therefrigerant temperatures measured at the corresponding sites are denotedas TK₁ to TK₆. These temperatures will be measured by thermocouples atthe appropriate locations.

Additional measurements of temperature take place upon outlet of thematerial from the single process stages; reference numbers .[.20.]..Iadd.30.Iaddend., 40 or 48 refer to temperatures Tm₂, Tm₃, Tm₄.Furthermore, at the same locations, the pressure or pressure differencewill also be measured (Pm₁, Pm₂ or Pm₃) to determine the consistency(viscous pressure drop).

A measurement of the power or torque Md₁ to Md₃ and measurements of therpm n₁ to n₃, are performed for the drive units of the single processstages, reference numbers 1 to 3.

For the dosed in starting components (fluid, gas), both the volumetricflow V_(L) and V_(g) are determined at 27 and 28, and also for the gas,the dosing pressure P_(g) is determined at 28, and for the mixture ofthe starting components at position 26, the mixing temperature Tm₁ isdetermined.

In the final process step (deep freezer stage), in order to check thetemperature profile, the temperature of the deeply frozen material isdetermined throughout the duration of the process stage at threeadditional locations (Tm₅ to Tm₇).

The target parameters in the manufacturing process of deep frozen foammaterials are the temperature of the material Tm₄ at the outlet of thedeep freezer stage, and the pressure or pressure difference Pm₃ (viscouspressure loss) measured at this location, which are a measure for theconsistency of the deeply frozen foamed matrix exiting the system. Todetermine the defined target parameters, the following predeterminedparameters are to be adjusted, according to the practical experience offormula development, and their constancy will be checked or controlled:fluid and gas volumetric flow V_(L) and V_(g), gas pressure .[.P_(L) .]..Iadd.P_(g) .Iaddend., performance data on the drive units Md₁ to Md₃and n₁ to n₃, and also the inlet temperatures of the refrigerant in thesingle process stages TK₂ ; TK₄ ; TK₆ and the mixture inlet temperatureTm₁ at 26, and also the back pressure in the aeration stage Pm₁.

As pure control parameters, the coolant outlet temperatures will bedetermined from the single process stages TK₁ ; TK₃ ; TK₅, and also themass temperatures Tm₂, Tm₃, Tm₄, Tm₅, Tm₆ and Tm₇, and the outletpressure Pm₂ from the prefreezing stage.

The decisive control quantities for the foam aeration are the volumetricflows of gas and fluid V_(g), V_(L) ; decisive for the setting of theconsistency-target parameters Pm₃ ; Tm₄ --are the power inlets in thesingle process stages Md₁ to Md₃ ; n₁ to .[.n₃ and.]. .Iadd.n₃ and.Iaddend.also the speed of the cooling process in the deep freezerstage, which is determined essentially by the inlet temperature of thecooling fluid TK₆ (reference number 44).

FIG. 4 shows a partial front view of the double screw system of thepresent invention. In the present invention, the deep-freezer stage 3shown in FIG. 3 is provided with at least one double screw system(double screw extruder) that has two screws 52 and 53 meshing lightlywith each other. The screws 52 and 53 are seated in the illustrateddesigns in one particular housing 54. The housing can be made of ametallic material, for example, steel; in particular, a highly alloyedstainless steel.

The two screws 52 and 53 will be driven by a drive unit (notillustrated), for example, jointly or individually by one motor,preferably via an elastic rotary coupling (not illustrated). Ifnecessary, an additional reducing gear can also be provided (also notillustrated).

When referring to "light screw meshing," it is meant that the lands ofthe screws (helices) 55 or 56 preferably do not intermesh very much,that is, the spacing of the rotary axis A of screws 52 .[.ad.]..Iadd.and .Iaddend.53 will be selected so that the lands (helices) 55and 56 are positioned with an increased spacing from the surface of thecylinder mantle 58 or 57 of the screws 52 and 53.

Furthermore, the axial positioning of the two screws 52 and 53 isdetermined preferably such that the helix 55 of the screw 52 penetratesto the middle axial region of helix 56 of the screw 53. This contributesto the avoidance of super-critical stresses of the energy input viashearing.

The screw channel of each screw 52 and 53 is of extremely flat design(H/W ≈0.1; see FIG. 8). The screw pitch ⊖ can also be 20° to 30° in thiscase.

The helices 55 and 56 scrape against the inner surface of the cylindermantle 59 or 60 and are thus of a relatively sharp edged design. Apartial, longitudinal section of the double screw system of FIG. 4 isshown in FIG. 5.

In the embodiment shown in FIG. 6, numerous coolant channels 61 areprovided in the housing 54 in parallel and positioned at a distance fromeach other, and a suitable refrigerant fluid flows through them in orderto deep cool and transport off the aerated and prefrozen foam (forexample, ice cream) that is mixed and conveyed from the screws 52 and53; this deep cooling shall take place to below -10° C., preferably to-16° C. to -45° C., especially to -18° C. to -20° C., at storagetemperature. An intensification of the cooling, and an improvement inthe homogeneity of the heat elimination will be achieved by anadditional inner cooling of the hollow designed screw shafts 66.

Similarly, in the embodiment shown in FIG. 7, the housing 54 is designedin a roughly flat-oval cross section, with semicircular arcs whose endsare joined by parallel straight lines separated at a distance from eachother. The housing 54 is located in a tubular, inner and outercylindrical container 65 that is partly filled with a refrigerant fluid62, for example, FRIGEN (TM), brine or the like, and that flushes thehousing 54 in order to the cool the foam to be mixed by the screws 52and 53, for example, whipped cream or ice cream, to storage temperature.Since for the optimum production of a creamy material system, forexample, for ice cream, a higher dispersed air fraction is needed, thegas preservation during the mechanical deep freezing treatment processmust be assured in the double screw system. Therefore, the shaft endprotruding from the housing 54 is sealed to the outside by a gas-tightrotary mechanical seal 64. Of the shaft ends, only the shaft end 63 inFIG. 9 is provided with a reference number. The other shaft end and thehidden gas-tight rotary mechanical seal are also designed with designdetails similar to those presented in FIG. 9.

Further modifications and alternative embodiments of the device of thepresent invention will be apparent to those skilled in the art in viewof the foregoing description. Accordingly, this description is to beconstrued as illustrative only and is for the purpose of teaching thoseskilled in the art the manner of carrying out the invention. It has beenunderstood that the forms of the invention herein shown and describedare to be taken as the presently preferred embodiments. Various changesmay be made in the shape, size and arrangement of parts. For example,equivalent elements or materials may be substituted for thoseillustrated and described herein, parts may be reversed, and certainfeatures of the invention may be utilized independently of otherfeatures, all as would be apparent to one skilled in the art afterhaving the benefit of this description of the invention. The presentinvention is therefore intended to embrace all alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

    ______________________________________                                        List of Reference Numbers                                                     ______________________________________                                        1     Aeration System                                                         2      Cooling or freezing system (freezer)                                   3      System for transportation and deep-freezing, combined                         extruder system, deep-freezing stage                                   4      Foam, product                                                          5      Shaft                                                                  6        Rotor                                                                7        Vanes                                                                8        Stator                                                               9        Vanes                                                                10         Foam, prefrozen                                                    11         Chamber                                                            12         Cooling system                                                     13     Cooling coils                                                          14       Extruder screw                                                       15         Housing, tubular                                                   16         Housing, tubular                                                   17         Housing, inner                                                     18         Annular chamber                                                    19         Refrigerant feed line                                              20         Cooling discharge nozzle                                           21         Rotor                                                              22         Vane                                                               23         Shaft                                                              24         Inner wall                                                         25         Vane                                                               26         Feed line                                                          27         End                                                                28         Pipe piece                                                         29         Inner chamber                                                      30         Pipe nozzle                                                        31         Direction indicated by arrow                                       32         Pipe nozzle                                                        33         Housing                                                            34         Annular chamber                                                    35         Feed line                                                          36         Annular chamber                                                    37         Runoff line                                                        38         Rotor                                                              39         Shaft                                                              40     Nozzle                                                                 41     Connecting nozzle                                                      42     Housing                                                                43         Annular chamber                                                    44         Line                                                               45         Line                                                               46         Shaft                                                              47         Conveying screw                                                    48         Nozzle                                                             49         Thermocouple                                                       50         Thermocouple                                                       51         Thermocouple                                                       52         Screw                                                              53         Screw                                                              54         Housing                                                            55         Land of the screw, helix                                           56         Land of the screw, helix                                           57         Cylinder mantle surface                                            58         Cylinder mantle surface                                            59         Cylinder mantle surface, inner                                     .[.59a                                                                              Cylinder mantle surface, inner.].                                       60         Refrigerant                                                        61         Refrigerant channel                                                62         Coolant                                                            63         Shaft end                                                          64         Rotary mechanical seal, gas-tight                                  65         Container                                                          66         Screw hollow shaft as refrigerant channel (possibly also                  heating medium for thawing)                                            Md.sub.1                                                                             Torque on shaft 23                                                     Md.sub.2                                                                             Torque on shaft 39                                                     Md.sub.3                                                                             Torque on shaft 46                                                     n.sub.1                                                                               Speed of shaft 23                                                     n.sub.2                                                                               Speed of shaft 39                                                     n.sub.3                                                                               Speed of shaft 46                                                     P.sub.g                                                                               Pressure of carrier gas fed in pipe 28                                .[.P.sub.L                                                                          Gas pressure.].                                                         Pm.sub.1                                                                                Pressure in pipe nozzle 30                                          Pm.sub.2                                                                                Pressure in nozzle 40                                               Pm.sub.3                                                                               Pressure in nozzle 48                                                Tm.sub.1                                                                               Temperature in tbe infeed line 26                                    Tm.sub.2                                                                                Temperature in the pipe nozzle 30                                   Tm.sub.3                                                                               Temperature in the nozzle 40                                         Tm.sub.4                                                                               Temperature in the nozzle 48                                         Tm.sub.5                                                                               Temperature at the thermocouple 49                                   Tm.sub.6                                                                                 Temperature at the thermocouple 50                                 Tm.sub.7                                                                                Temperature at the thermocouple 51                                  TK.sub.1                                                                            Temperature in the refrigerant runoff nozzle 20                         TK.sub.2                                                                            Temperature in the refrigerant inlet line 19                            TK.sub.3                                                                            Temperature in the line 37                                              TK.sub.4                                                                            Temperature in the inlet line 35                                        TK.sub.5                                                                            Temperature in the line 45                                              TK.sub.6                                                                            Temperature in the line 44                                              V.sub.L                                                                              Volume flow of the fluid at the inlet of line 27                       V.sub.g                                                                              Volume flow of the carrier gas at the inlet of line 28                 A      Spacing of rotational axis of screws 52 and 53                         D      Cylinder diameter                                                      H      Channel height                                                         L      Axial channel height                                                   W      Channel width                                                          e      Land of the screw                                                      θ                                                                              Screw pitch angle                                                      .[.p  Number of channels (number of slots).].                                 .[.P  Screw pitch (= p*L).].                                                  ______________________________________                                    

What is claimed is:
 1. A device for the cooling of edible foams,comprising:a cooling system for pre-freezing an edible foam; an aerationsystem outlet-connected to said cooling system; a motor-driven extruderdevice designed as a combined deep freezing and transport deviceoutlet-connected to said cooling system for cooling pre-frozen ediblefoam to a storage temperature, wherein said extruder device has at leastone double screw system comprising:two screws each having a shaftcylinder with a mantle surface on which the threads of the screws aredisposed, said screws being positioned parallel to each other with theirrotational axes and being further positioned such that the threads ofthe second screw are centered between the threads of the first screw andan increased spacing of the rotational axes of the screws is created,such that the front side of the screw thread of the other screw facingthe surface of the cylinder mantle of each screw has a radial distancefrom it; a housing enclosing said screws, said housing having an innermantle surface proximate to said screws, wherein the threads of saidscrews are positioned so as to scrape against the inner mantle surfaceof said housing; and wherein the threads of the screws with the surfaceof the cylinder mantle of the screws and of the inner mantle surface ofthe housing .[.bounds.]. .Iadd.bound .Iaddend.an extremely flat screwchannel.
 2. The device of claim 1, wherein:a ratio of the channel heightto the channel width for each said screw is approximately 0.1; and ascrew pitch angle for each said screw is between approximately 20° and30°.
 3. The device of either of claims 1 or 2, said housing having aplurality of refrigerant channels positioned parallel to the axes ofrotation of said screws and positioned at a distance relative to eachother.
 4. The device of either of claims 1 or 2, wherein the shafts ofsaid screws are substantially hollow.
 5. The device of any of claims 1or 2, wherein said housing is sealed by a gas-tight, rotating mechanicalseal.
 6. The device of any of claims 1 or 2, further comprising acontrol unit for controlling the speed of rotation of said screw system,whereby the consistency of the foam is determined by means of an on-lineviscosity measurement in such a manner that the mechanical energydissipated in the material system--that is, mechanical energy convertedinto heat energy--does not exceed a critical amount.
 7. The device ofany of claims 1 or 2, further comprising a control unit for controllingthe speed of rotation of said screw system specifically according to theformula under consideration of the temperature-related, critical shearstresses for the structural changes for optimum tailoring of mechanicalenergy input, homogeneous stress on the particular foam, super-criticalshear, cooling gradient and freezing process, by means of acquisition ofthe foam consistency as target parameter, whereby the productconsistency is determined by means of an on-line viscosity measurementin such a manner that the mechanical energy dissipated in the materialsystem--that is, mechanical energy converted into heat energy--does notexceed a critical amount. .Iadd.
 8. Motor-driven extruder device forfreezing and transporting an edible food product comprising incombination: two screws each having a shaft cylinder with a mantlesurface on which the threads of the screws are disposed, said screwsbeing positioned parallel to each other with their rotational axes andbeing further positioned such that the threads of the second screw arelocated between the threads of the first screw; a housing enclosing saidscrews, said housing having an inner mantle surface proximate to saidscrews, wherein the threads of said screws are positioned so as toscrape against the inner mantle surface of said housing, wherein thethreads of the screws with the mantle surfaces of the screws and of theinner mantle surface of the housing bound an extremely flat screwchannel; and means for cooling the housing to a temperature for freezingthe food product that is mixed and conveyed by thescrews..Iaddend..Iadd.9. The device of claim 8 wherein the shafts areprovided with additional, inner cooling..Iaddend..Iadd.10. The device ofeither of claim 8 or 9 wherein the cooling means comprises a pluralityof refrigerant channels positioned parallel to the axes of rotation ofsaid screws and positioned at a distance relative to each other, with asuitable refrigerant fluid flowing through the refrigerantchannels..Iaddend..Iadd.11. The device of claim 9 wherein the shafts ofsaid screws are substantially hollow..Iaddend..Iadd.12. The device ofclaim 8 wherein the threads of the second screw are centered between thethreads of the first screw and an increased spacing of the rotationalaxes of the screws is created, such that the front side of the screwthread of the other screw facing the surface of the cylinder mantle ofeach screw has a radial distance from it..Iaddend..Iadd.13. The deviceof claim 8 wherein a screw channel for each screw between the threads ofthe screw, the inner mantle surface of the housing, and the mantlesurface of the screw is extremely flat..Iaddend..Iadd.14. The device ofclaim 13 wherein a ratio of the height to the width of the screw channelfor each screw is approximately 0.1..Iaddend..Iadd.15. The device ofclaim 14 wherein a screw pitch angle for each screw is between 20° and30°..Iaddend..Iadd.16. The device of claim 8 wherein the cooling meanscomprises a tubular container partly filled with a refrigerant fluid,with the housing located within the tubular container, with therefrigerant fluid flushing the housing..Iaddend..Iadd.17. The device ofclaim 8 wherein each of the screws include a shaft end protruding fromthe housing; and wherein the device further comprises, in combination: agas-tight rotary mechanical seal for sealing the shaft end to thehousing to assure gas preservation in the housing during freezing andtransporting of the edible food product..Iaddend..Iadd.18. Method forproducing a frozen edible food product comprising the steps of:providing an extruder device including two screws each having a shaftcylinder with a mantle surface on which the threads of the screws aredisposed, said screws being disposed parallel to each other with theirrotational axes, said screws being further positioned such that thethreads of the second screw are located between the threads of the firstscrew, with the extruder device further including a housing enclosingsaid screws, said housing having an inner mantle surface proximate tosaid screws, wherein the threads of said screws are positioned so as toscrape against the inner mantle surface of said housing, wherein thethreads of the screws with the mantle surfaces of the screws and of theinner mantle surface of the housing bound an extremely flat screwchannel; cooling the housing to a temperature for freezing the foodproduct; supplying an edible food product into the housing; and rotatingthe two screws within the housing while the edible food product is beingsupplied into the housing for freezing, mixing, and conveying the ediblefood product..Iaddend..Iadd.19. The method of claim 18 wherein thesupplying step comprises the step of supplying the edible food productin the form of an edible foam into the housing..Iaddend..Iadd.20. Themethod of claim 19 wherein the supplying step further comprises the stepof cooling the edible foam before supplying to thehousing..Iaddend..Iadd.21. The method of claim 18 further comprising thestep of inner cooling the shaft cylinders of the twoscrews..Iaddend..Iadd.22. The method of claim 21 wherein the innercooling step comprises the steps of: providing refrigerant channels inthe shaft cylinders of the two screws; and flowing a refrigerant fluidthrough the refrigerant channels..Iaddend..Iadd.23. The method of claim18 wherein the cooling step comprises the steps of: providing aplurality of refrigerant channels in the housing positioned parallel tothe axes of rotation of said screws and positioned at a distancerelative to each other; and flowing suitable refrigerant fluid throughthe refrigerant channels..Iaddend..Iadd.24. The method of claim 18wherein the providing step comprises the step of providing the extruderdevice wherein the threads of the second screw are centered between thethreads of the first screw and an increased spacing of the rotationalaxes of the screws is created, such that the front side of the screwthread of the other screw facing the surface of the cylinder mantle ofeach screw has a radial distance from it..Iaddend..Iadd.25. The methodof claim 18 wherein the providing step comprises the step of providingthe extruder device wherein a screw channel for each screw between thethreads of the screw, the inner mantle surface of the housing, and themantle surface of the screw is extremely flat..Iaddend..Iadd.26. Themethod of claim 18 wherein the providing step comprises the step ofproviding the extruder device wherein a ratio of the height to the widthof the screw channel for each screw is approximately0.1..Iaddend..Iadd.27. The method of claim 18 wherein the providing stepcomprises the step of providing the extruder device wherein a screwpitch angle for each screw is between 20° and 30°..Iaddend..Iadd.28. Themethod of claim 18 wherein the providing step comprises the step ofproviding the extruder device wherein each of the screws includes ashaft end protruding from the housing; and wherein the extruder devicefurther includes a gas-tight rotary mechanical seal for sealing theshaft end to the housing to assure gas preservation in the housingduring rotation of the two screws..Iaddend..Iadd.29. The method of claim18 wherein the cooling step comprises the steps of: providing a tubularcontainer, with the housing located within the tubular container; andfilling the tubular container with a refrigerant fluid for flushing thehousing..Iaddend.